The installation of a work platform according to the above is a difficult operation requiring favorable weather conditions and very large efforts in vessels, equipment and personnel.
In a prior art example of a tension leg moored platform, the platform is positioned in an exact position above its sea bed anchor template. Then a number of tendon strings are lowered down from the bottom of each respective column, with the same technique as a drill string, i.e. short sections are added while the string is lowered down from a derrick-like device in each column. Each of these strings should "target" its special anchoring point in the template. This complicated method normally takes several days and requires very good weather, small waves and considerable assistance in the form of stable anchored barges, serving as dampers for pendulum motions.
As an alternative to this prior art tether system, it has been proposed in U.S. Pat. No. 4,418,147 to prefabricate the tendons in full length and pre-install them at the sea bed anchor template, whereafter the platform can be moved out to the location and be connected to the upper ends of the tendons. Also this tether system is dependant upon good weather and small waves. Besides, a comprehensive system of wire lines must be used for guiding both ends of the tendons into their respective locations. Special problems may arise when it is time to exchange one of the tendons while the platform is on its location.